The present invention relates to injection presses for molding pieces of elastomer.
More particularly, the invention relates to an injection press for molding pieces of elastomer and comprising:
first and second substantially parallel platens slidably displaceable relative to each other along a central axis between a closed position in which said first and second platens are relatively close to each other and an open position in which said first and second platens are further apart from each other;
a molding device comprising at least one mold, itself comprising two mold portions that are movable relative to each other along said central axis between a closed position in which said two mold portions are in closed contact to enable at least one elastomer piece to be molded, and an open position enabling said elastomer piece to the unmolded, said molding device being placed between the first and second platens;
an injector device adapted to inject elastomer into the mold;
at least one heater device adapted to heat the elastomer contained in the mold in order to vulcanize it; and
a control device comprising at least one jack adapted to move the first and second platens between their open and closed positions.
Known presses of that type make it possible for the cavities to be unmolded only all together, once all of the molded elastomer pieces have been injected and vulcanized in the cavities of the molding device. Those presses thus have an operating cycle that is quite long, given that vulcanization can last for several minutes. To compensate for that handicap, the molding device generally has a large number of cavities (for example 16 cavities) in order to make it possible to achieve a fairly high rate of production.
Those known presses give satisfaction as to the effectiveness with which the molding device is closed and as to their compactness.
Nevertheless, they suffer from the following drawbacks:
their elastomer injector devices are particularly expensive insofar as they must be capable of filling a large number of cavities simultaneously;
their injector devices are used for a small fraction of the time only, and are therefore not very productive, which is particularly troublesome in equipment that is expensive, as mentioned above;
since the molding device has a large number of cavities, the cavities are connected to an injector device via relatively long lengths of feed channel, thus giving rise to significant losses of material during molding: the elastomer present in such channels is itself vulcanized while the molded pieces are vulcanizing, and the vulcanized rubber present in the channels at the end of molding cannot be recycled; and
because of the great length of the feed channels, the elastomer needs to be injected at a temperature that is relatively low in order to ensure that it does not begin to vulcanize in the channels before it has filled the cavities: this gives rise to vulcanization that is slower, since longer heating is required in the cavities.
A particular object of the present invention is to mitigate those drawbacks.
To this end, according to the invention, in an injection press of the kind in question:
the molding device includes a turret which is rotated by a shaft disposed on said central axis and which carries a number n not less than 2 of independent molds, the molds being movable by rotation of the turret between a number p of fixed stations, where p is not less than n, and these stations include at least one injection station and an unmolding station; and
when they are in the closed position, the first and second platens are adapted to clamp against each other in the closed position the two mold portions belonging to each mold that is in a station other than the unmolding station, while enabling a mold that is in the unmolding station to be opened.
By means of these dispositions, each mold is caused to pass in succession through the various stations of the injection press. During each of these movements, the elastomer piece(s) present in the mold that is in the unmolding station is/are unmolded.
This makes it possible to obtain rates of throughput that are quite high without it being necessary to use molds having numerous cavities. It is thus possible to use an elastomer injector device that is of low cost. In addition, this also makes it possible to limit the length of the cavity feed channels within the molds, thus serving firstly to limit losses of material, and secondly to enable the elastomer to be injected at a higher temperature, giving rise to vulcanization that takes place more quickly.
Finally, the injector devices of presses of the invention are in use during a large fraction of the time, and are therefore more productive.
In preferred embodiments of the invention, use can optionally be made of one or more of the following dispositions:
the control device is adapted cyclically to move the first and second platens apart, to turn the turret so as to cause the molds to pass from one station to another, and then to move said first and second platens towards each other so as to clamp the two mold portions against each other in the closed position for each mold that is to be found in a station other than the unmolding station;
the first and second platens are stationary in rotation about the central axis and at least one of the first and second platens presents a notch corresponding with the unmolding station to enable the mold that is in the unmolding station to be opened while said first and second platens are in their closed position;
the first platen is slidably mounted on peripheral columns parallel to the shaft and placed around the turret;
the first platen is slidably mounted on a fixed structure secured to the second platen, the central axis is substantially vertical, the first platen is placed beneath the second platen, the turret is mounted to slide freely with lost motion on the shaft, said shaft including an abutment which limits downward sliding of the turret, and the control device is adapted to lower the first platen sufficiently to enable the turret to come to bear against said abutment of the shaft and to ensure that the molding device is not in contact with the first and second platens when said first and second platens are in the open position;
the number p of stations is equal to the number n of molds;
the number n of molds is not less than four;
the stations comprises pxe2x88x922 vulcanization stations;
at least some stations include heater devices (the heater devices are thus stationary, which avoids the need to use rotary electrical connections);
at least some of the heater devices of the stations comprise respective heater surfaces secured to one of said first and second platens;
each mold is adapted to mold simultaneously a number of elastomer pieces lying in the range 1 to 4;
each mold portion comprises an outer shell fixed to the turret and a block which is supported by said shell and which presents an inside shape complementary to the elastomer piece to be molded;
the control device comprises at least first and second jacks, the first jack being placed to correspond with the injection station and the second jack being diametrically opposite the first jack about the central axis; and
each mold comprises a top mold portion and a bottom mold portion, and the unmolding station has a mold opening device adapted to raise the top mold portion to separate it from the bottom mold portion.